The present invention relates generally to fiber optics, and more specifically to liquid-core fiber optics having a flowing liquid core.
Fiber optics transmit light axially while confining it radially. Light is transmitted through a transparent core and confined by total internal reflectance at the interface of a core having a high index of refraction surrounded, clad, or sheathed by material of a lower index of refraction. While most fiber optic cores are solid, this is not a requirement. Liquid-core fiber optics were developed and demonstrated in the past primarily for their low transmission loss. As transmission losses through solid-core silica fibers were brought down over time, interest in liquid-core fiber optics declined.
Conventional solid-core fiber optics have been used for a number of years as sensors for determining strain, temperature and a variety of other physical parameters. Typically, a change in a particular physical parameter can be made to cause a corresponding change in the index of refraction of the fiber optic core which can then be measured by a variety of methods.
More recently, liquid-core fiber optics have been used to measure temperature. For example, Geddes et al., in U.S. Pat. No. 4,201,446, describe a liquid-core fiber optic in which the refractive index of the liquid core varies with temperature. The temperature of the substance through which the liquid-core optical fiber passes can be measured from the maximum angle of the transmitted light output from the end of the liquid-core optical fiber. Kuribara et al., in "Liquid core optical fibre for voltage measurement using Kerr effect," Elec. Lett., 19, pp. 133-135, 1983, used hollow-core fibers filled with Kerr liquids for voltage measurement. Hartog, in "A distributed temperature sensor based on liquid-core optical fibers," J. Lightwave Tech., LT-1, pp. 498-509, 1983, followed with a distributed temperature measurement technique that used optical time domain reflectometry (OTDR) techniques to scan the backscatter from a liquid as a function of temperature.
The possibility of flowing the liquid through an optical fiber in a liquid-core fiber optic has been explored in, for example, U.S. Pat. No. 5,165,773 to Nath. As part of his invention, Nath describes a light guide for use with an endoscope in which saline is used as the liquid core and is slowly flowed through the light guide into a body cavity, thus preventing contamination of the end of the light guide by coagulated tissue, blood or the like.
Unfortunately, the prior art has generally failed to take full advantage of all the useful possibilities from the ability of the liquid in a liquid-core fiber optic to flow through the fiber.
It is, therefore, a principal object of the present invention to provide liquid-core fiber optics that take fuller advantage of the ability of a liquid core to flow through the fiber.
It is a specific object of the present invention to provide liquid-core fiber optics that use a flowing liquid core for heat transfer between the fiber and a structural component or substance with which it is in contact.
It is a feature of the present invention that it can combine its heat exchange function with temperature and strain sensing and with any other parameter measuring features of prior art solid-core and liquid-core fiber optics.
It is an advantage of the present invention that it can provide either heating or cooling while measuring physical parameters.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.